In the construction of residential and commercial buildings it is common to have back-to-back bathrooms wherein the hot and cold water supply pipes service shower and tub units on opposite sides of the wall. Prior art shower control valves often have the cold water inlet on one side and the hot water inlet on the other side. As the two supply pipes in the wall are normally side-by-side, it is necessary to provide an awkward cross-over arrangement for one of the shower units. Later inventions provided shower control valve assemblies that utilise a casing having two inlets and a replaceable cartridge unit which can be adjusted in a relatively simple manner at the time of installation so that it is entirely optional as to which of the inlets is connected to the hot water supply pipe and which is connected to the cold water pipe. Commonly assigned Canadian Patent No. 1,050,853 of Mar. 20, 1979 discloses just such an arrangement. The valve assembly of that patent is pressure balanced, with a single handle to control the temperature and the pressure of the water issuing from the shower. The casing of the patented valve assembly included a single outlet leading to the shower, water for the tub flowing through a separate spout having a diverter valve associated therewith.
The trend in pressure balanced valve assemblies has been towards single handle control valves which are also adapted to control the flow of water to a tub as well as to a shower. U.S. Pat. Nos. 4,681,140; 4,901,750; and 4,905,732 all teach single handle pressure, temperature and/or volume balanced mixing valves.
One of the problems associated with any water flow arrangement is that of water hammer, generated noise which is frequently experienced in pressure sensing mixing valves when they are installed in line with quick closing faucets. Other problems involve cross flow between the hot and cold water supply lines; back flow in either or both of the supply lines; and wear of the rubber seal that contacts the mixing disc of the valve.
Commonly assigned Canadian Patent Application No. 2,076,924 filed Aug. 26, 1992 teaches a single handle pressure and temperature balancing mixing valve assembly that includes, among other features, a check valve at each of the hot and cold water inlets to prevent cross flow between the hot and cold water supply lines, to prevent back flow to either supply line, and to eliminate the effects of water hammer. Additionally, or optionally, the valve casing may include separate outlets for the tub and for the shower, with there being a built-in bypass or diverter channel to divert water from one outlet to the other and the entire valve cartridge may be rotated through 180.degree. to reverse the hot and cold inlets.
Sealing of the water at the rotatable mixing valve disc in the aforementioned design is achieved through the utilization of cup-shaped rubber washers or glands which seal against the mixing disc. The disc can rotate through about 270.degree. and the rubber washers are always in contact with the disc, held thereagainst by a spring and available water pressure. The rotational movement of the disc causes wear on the rubber washers. This problem may be overcome in some applications by the use of internal lubrication with a wax material. This lubrication solves the wear problem and reduces the torque required to turn the valve on and off. However, such internally lubricated washers usually do not qualify for contact with potable water due to bacterial growth and toxicity.